System and method for reducing hydrogen in a casting

ABSTRACT

A method involves filling a hydrogen-lean molten material in a crucible and closing a lid of the crucible and then feeding a first quantity of a compressed dry gas via the crucible to form a dry gas blanket on a surface of the hydrogen-lean molten material. The method further involves feeding a second quantity of the compressed dry gas to a mold assembly to purge the mold assembly and transferring the hydrogen-lean molten material via an opening of the lid of the crucible to a mold cavity of the mold assembly. The method further involves cooling the hydrogen-lean molten material to form a casting.

BACKGROUND

The invention relates generally to molding techniques, and more particularly to a system and method for reducing hydrogen in a casting, for example, an aluminum casting.

Fabrication processes are used to shape, machine, and join metals or metal alloys. One fabrication process involves using a molding process to produce the desired shape of the metal or metal alloy. The molding process involves heating metal to a molten state, pouring the molten metal into a mold, and allowing the molten metal to cool and solidify in the shape of the mold. Castings obtained by the molding processes may be used in areas such as transportation, aerospace, defense, mining, construction, maritime, fluid power, and domestic household, and the like.

A sand molding process involves using a pattern, which is a replica of the finished casting. The pattern is slightly larger to allow for material shrinkage during solidification and cooling. The pattern (made of wood, plastic, or metal) can either be disposed loose or attached to a plate. A flask is disposed around the pattern to contain the prepared, free-flowing molding sand that is placed on the pattern. Pressure is applied to the sand to compact the sand firmly against the face of the pattern. When the sand is compacted, the sand exhibits physical properties that allow holding the exact shape of the pattern after the pattern is drawn from the mold. When the casting is solidified, the sand is removed from the casting.

In foundries, inert gases are purged through molten melt to scavenge hydrogen and to improve the quality of the casting. Such a process is referred to as “hydrogen degassing”. After degassing treatment, the molten metal tends to re-pickup hydrogen by reacting with surrounding hydrogen-containing gases during metal transfer and mold filling processes. Such a hydrogen re-pickup may not be undesirable to the quality of the casting but may be truly detrimental to cryogenic applications where cast components may outgas and impact the cryogenic system performance.

It is desirable to have a system and method for reducing hydrogen in a casting.

BRIEF DESCRIPTION

In accordance with one exemplary embodiment, a method is disclosed. The method involves filling a hydrogen-lean molten material in a crucible and closing a lid of the crucible and then feeding a first quantity of a compressed dry gas via the crucible to form a dry gas blanket on a surface of the hydrogen-lean molten material. The method further involves feeding a second quantity of the compressed dry gas to a mold assembly to purge the mold assembly and transferring the hydrogen-lean molten material via an opening of the lid of the crucible to a mold cavity of the mold assembly. The method further involves cooling the hydrogen-lean molten material to form a casting.

In accordance with another exemplary embodiment, a system is disclosed. The system includes a crucible with a lid, the crucible utilized to store a hydrogen-lean molten material. The system further includes a mold assembly comprising a mold cavity, the mold cavity receiving the hydrogen-lean molten material from the crucible and cooling the hydrogen-lean molten material to form a casting. The system further includes a gas source to feed a first quantity of a compressed dry gas via the crucible to form a dry gas blanket on a surface of the molten material and to feed a second quantity of the compressed dry gas to a mold assembly to purge the mold assembly.

DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic representation of a system for molding a hydrogen-lean molten material in accordance with an exemplary embodiment;

FIG. 2 is a schematic representation of a system for molding a hydrogen-lean molten material in accordance with an exemplary embodiment of FIG. 1;

FIG. 3 is a schematic representation of a system for molding a hydrogen-lean molten material in accordance with another exemplary embodiment; and

FIG. 4 is a schematic representation of a system for molding a hydrogen-lean molten material in accordance with an exemplary embodiment of FIG. 3; and

FIG. 5 is a sectional view of a casting molded in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

In accordance with certain embodiments of the present invention, a method for molding a hydrogen-lean molten material is disclosed. The method involves filling a hydrogen-lean molten material in a crucible and then closing a lid of the crucible. The method further involves feeding a first quantity of a compressed dry gas via the crucible to form a dry gas blanket on a surface of the hydrogen-lean molten material. The method also involves feeding a second quantity of the compressed dry gas to a mold assembly to purge the mold assembly. Further, the method involves transferring the hydrogen-lean molten material via an opening of the lid of the crucible to a mold cavity of the mold assembly and cooling the hydrogen-lean molten material to form a casting. The exemplary method involves minimizing a hydrogen content in the casting by controlling environment within the crucible and the mold assembly. In one embodiment, the casting is a low cryogenic magnet coil former. In such an embodiment, outgassing of hydrogen from the low cryogenic magnet coil former during storage and transportation is minimized. In accordance with certain other embodiments of the present invention, a system for molding a hydrogen-lean molten material is disclosed.

FIG. 1 is a schematic representation of a system 10 for molding a hydrogen-lean molten material 12 in accordance with an exemplary embodiment. In the illustrated embodiment, the system 10 includes a crucible 14, a mold assembly 16, and a gas source 18. The crucible 14 includes a container 20 provided with a heating element 22 and a lid 24. The heating element 22 is used to maintain the material 12 in a molten state within the container 20. In one embodiment, the hydrogen-lean molten material 12 may include a metal such as aluminum. In another embodiment, the hydrogen-lean molten material 12 may include a metal alloy. The lid 24 has an opening 26 which is closed using a removable stopper 28.

The mold assembly 16 has a mold cavity 30 for molding the hydrogen-lean molten material 12 to form a casting. In one embodiment, the casting may be a low cryogenic magnet coil former. In the illustrated embodiment, a fill pipe 32 is coupled to the mold cavity 30. The mold cavity 30 may be optionally coupled to a vacuum source 33 for applying a vacuum force to the mold cavity 30. The gas source 18 includes two containers 34, 36 filled with a compressed dry gas 38. The compressed dry gas 38 may include at least one of argon, air, nitrogen, or the like. The gas source 18 further includes connecting pipes 40, 42 coupled respectively to the two containers 34, 36. The pipes 40, 42 are further provided with regulators 44, 46 respectively for controlling flow of the compressed dry gas 38 through the pipes 40, 42. The gas source 18 is used to feed the compressed dry gas 38 to the crucible 14 and the mold assembly 16.

Now referring to an exemplary method of casting, the hydrogen-lean molten material 12 is filled in the container 20 of the crucible 14 and the lid 24 is closed. As discussed earlier, the heating element 22 is used to maintain the material 12 in a molten state. Thereafter, a first quantity of the compressed dry gas 38 from the container 34, is fed via the crucible 14 to form a dry gas blanket 48 on a surface 50 of the hydrogen-lean molten material 12. The hydrogen-lean molten material 12 is separated from the external environment by the dry-gas blanket 48 over the surface 50 of the hydrogen-lean molten material 12. The first quantity of the compressed dry gas 38 may vary depending upon the application.

Then, a second quantity of the compressed dry gas 38 is fed from the container 36 to the mold assembly 16 to purge the mold cavity 30. Specifically, the second quantity of the compressed dry gas 38 is fed via the fill pipe 32 to the mold cavity 30 to purge the mold cavity 30. Such purging facilitates to maintain a positive in-mold pressure until at least 95% of hydrogen-containing gases are removed from the mold cavity 30.

FIG. 2 is a schematic representation of a system 10 for molding a hydrogen-lean molten material 12 in accordance with an exemplary embodiment of FIG. 1. In the illustrated embodiment, the crucible 14 is positioned below and the mold assembly 16 is positioned above the crucible. The hydrogen-lean molten material 12 is fed into the mold cavity 30 via the fill pipe 32 under influence of a counter gravity force. Specifically, the mold assembly 16 is aligned with the crucible 14 and the stopper 28 is removed. Then, the fill pipe 32 is inserted via the opening 26 of the lid 24 into the hydrogen-lean molten material 12 filled in the container 20 of the crucible 14.

The hydrogen-lean molten material 12 is fed from the container 20 via the fill pipe 32 to the mold cavity 30 of the mold assembly 16. In one embodiment, the hydrogen-lean molten material 12 is fed from to the mold cavity 30 under the influence of the counter gravity force by applying a vacuum force from the vacuum source 33 (shown in FIG. 1) to the mold cavity 30. In another embodiment, the hydrogen-lean molten material 12 is fed from the mold cavity 30 under the influence of the counter gravity force by using a third quantity of the compressed dry gas 38 fed from the container 36 to the mold cavity 30. Thereafter, the hydrogen-lean molten material 12 is cooled in the mold cavity 30 to form a casting.

The hydrogen content in the casting is linearly proportional to a relative humidity of the process atmosphere. In accordance with the embodiments of the present invention, hydrogen content is reduced in the casting by reducing a moisture content in casting process environment using the compressed dry gas 38.

FIG. 3 is a schematic representation of a system 52 for molding a hydrogen-lean molten material 54 in accordance with another exemplary embodiment. In the illustrated embodiment, the system 10 includes a crucible 56, a mold assembly 58, and a gas source 60. The crucible 56 includes a container 60 provided with a heating element 62 and a lid 64. The lid 64 has an opening 66 which is closed using a removable stopper 68.

The mold assembly 58 has a mold cavity 70 for molding the hydrogen-lean molten material 54 to form a casting. In the illustrated embodiment, the mold assembly 58 has a pour cap 72 provided with a stopper 74. The stopper 74 has a passage 71 provided with a stopper 73. The mold cavity 70 may be optionally coupled to a vacuum source 76 for applying a vacuum force to the mold cavity 70. The gas source 60 includes two containers 78, 80 filled with a compressed dry gas 82. The gas source 60 further includes connecting pipes 84, 86 coupled respectively to the two containers 78, 80. The pipes 84, 86 are further provided with regulators 88, 90 respectively for controlling flow of the compressed dry gas 82 through the pipes 84, 86.

Now referring to an exemplary method of casting, the hydrogen-lean molten material 54 is filled in the container 60 of the crucible 56 and the lid 64 is closed. Thereafter, a first quantity of the compressed dry gas 82 from the container 80, is fed via the crucible 56 to form a dry gas blanket 92 on a surface 94 of the hydrogen-lean molten material 54.

Then, a second quantity of the compressed dry gas 82 is fed from the container 78 to the mold assembly 58 to purge the mold cavity 70. Specifically, the stopper 73 is removed and a second quantity of the compressed dry gas 82 is fed via the passage 71 to the mold cavity 70 to purge the mold cavity 30. Such purging facilitates to maintain a positive in-mold pressure until at least 95% of hydrogen-containing gases are removed from the mold cavity 70.

FIG. 4 is a schematic representation of a system 52 for molding a hydrogen-lean molten material 54 in accordance with an exemplary embodiment of FIG. 3. In the illustrated embodiment, the mold assembly 58 is positioned below and the crucible 56 is positioned above the mold assembly 58. The hydrogen-lean molten material 54 is fed into the mold cavity 70 under influence of a gravity force. Specifically, the stoppers 68 and 73 are removed and the hydrogen-lean molten material 54 is poured into the mold cavity 70 via the pour cap 72 by tilting the crucible 56. Thereafter, the hydrogen-lean molten material 54 is cooled in the mold cavity 70 to form a casting.

FIG. 5 is a sectional view of a casting 96 molded in accordance with an exemplary embodiment of the present invention. In the illustrated embodiment, the casting 96 is a low cryogenic coil former. As discussed previously, the hydrogen-lean molten material is fed to a mold cavity of the mold assembly. Thereafter, the hydrogen-lean molten material is cooled in the mold cavity to form the casting 96.

In accordance with the embodiments of the present invention, hydrogen content and an unpredictable variation of the hydrogen content in the casting due to weather changes are reduced. Hence, hydrogen outgassing from the casting, for example, an aluminum coil former, during storage and transportation is reduced. Additionally, issues associated with different amount of hydrogen content in castings such as coil formers cast at different seasons are avoided, thereby enhancing overall system reliability. Moreover, there is no requirement for usage of expensive hydrogen removal materials, such as palladium oxide.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. 

1. A method comprising: filling a hydrogen-lean molten material in a crucible and closing a lid of the crucible; feeding a first quantity of a compressed dry gas via the crucible to form a dry gas blanket on a surface of the hydrogen-lean molten material; feeding a second quantity of the compressed dry gas to a mold assembly to purge the mold assembly; and transferring the hydrogen-lean molten material via an opening of the lid of the crucible to a mold cavity of the mold assembly; and cooling the hydrogen-lean molten material to form a casting.
 2. The method of claim 1, wherein the hydrogen-lean molten material comprises a metal.
 3. The method of claim 1, wherein the hydrogen-lean molten material comprises a metal alloy.
 4. The method of claim 1, wherein the compressed dry gas comprises at least one of argon, air, and nitrogen.
 5. The method of claim 1, wherein transferring the hydrogen-lean molten material comprises transferring the hydrogen-lean molten material to the mold cavity of the mold assembly under influence of a counter gravity force.
 6. The method of claim 5, further comprising generating the counter gravity force by using a third quantity of the compressed dry gas.
 7. The method of claim 5, further comprising generating the counter gravity force by applying a vacuum force.
 8. The method of claim 1, wherein transferring the hydrogen-lean molten material comprises transferring the hydrogen-lean molten material to the mold cavity of the mold assembly under influence of a gravity force.
 9. The method of claim 1, wherein the casting comprises a low cryogenic magnet coil former.
 10. A system comprising: a crucible with a lid, the crucible utilized to store a hydrogen-lean molten material; a mold assembly comprising a mold cavity, the mold cavity receiving the hydrogen-lean molten material from the crucible and cooling the hydrogen-lean molten material to form a casting; and a gas source: to feed a first quantity of a compressed dry gas via the crucible to form a dry gas blanket on a surface of the molten material; and to feed a second quantity of the compressed dry gas to a mold assembly to purge the mold assembly.
 11. The system of claim 10, wherein the hydrogen-lean molten material comprises a metal.
 12. The system of claim 10, wherein the hydrogen-lean molten material comprises a metal alloy.
 13. The system of claim 10, wherein the compressed dry gas comprises at least one of argon, air, and nitrogen.
 14. The system of claim 10, wherein the crucible is configured to transfer the hydrogen-lean molten material to the mold cavity of the mold assembly under influence of a counter gravity force.
 15. The system of claim 14, wherein the gas source is configured to generate the counter gravity force by using a third quantity of the compressed dry gas.
 16. The system of claim 14, further comprising a vacuum source to apply a vacuum force to generate the counter gravity force.
 17. The system of claim 10, wherein the crucible is configured to transfer the hydrogen-lean molten material to the mold cavity of the mold assembly under influence of a gravity force.
 18. The system of claim 10, wherein the casting comprises a low cryogenic magnet coil former. 